End of the world: Why scientists fear sun will evolve to

The sun is the star at the centre of our solar system – the Milky Way.It is nearly a perfect sphere of hot plasma and is made up of roughly 74 per cent of hydrogen, 25 per cent of helium and 1 per cent of a mixture of elements. The star takes 600 tonnes of this hydrogen and fuses it into helium every second, converting matter into energy – or light and heat.

The sun currently sits in what is known as the main sequence, a band of stars in hydrostatic equilibrium – meaning it is resting at a constant point due to external forces such as gravity.

Louise Harra, Professor of Solar Physics at UCL Mullard Space Science Laboratory, revealed how it has been comfortably placed here for more than 4.5 billion years, but that will not last forever.

She told BBC Radio 4 listeners on a 2015 episode of "In Our Time" called "The sun" that it is "quite a boring star, really".

However, she added: "There is a lot of activity going on inside and you get a lot of dramatic explosions.”
Ms Harra went on to reveal how the sun could come to the end of its life.

She continued: “It’s halfway through its life now, it lays on the main sequence and that’s where 90% of stars are when they convert hydrogen to helium.

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“But if the star is not big enough to create fusion then it does not have enough energy to create light.

“It is about 4.5 billion years old and it has about 5.5 billion to go.

“The main sequence is just the lifetime of the star – its ability to convert hydrogen to helium.”
This idea is known as the core hydrogen exhaustion and it is one of the possible ends to life on Earth.

Scientists have previously revealed that the sun does not have enough mass to explode into a supernova.

Therefore, it will exit the main sequence in roughly 5 billion years, becoming a red giant.

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